We demonstrate optical bistability in InP/InAlGaAs multi-quantum well(MQW) semiconductor ring lasers(SRL) which
are fabricated by the use of inductively coupled plasma reactive ion etching (ICP-RIE) and can be used in a multi-ring to
achieve all-optical storage. Unlike other international reports, the observed optical bistability has unidirectional regime
started directly from the threshold, skip the first two regimes and greatly reduce the injection current required in
applications. The device described in this article achieves threshold current 56mA which is quite low compared to other
reported devices, and some analysis and experiments on the etching depth have been done.
A novel Si LED with three terminals has been designed and fabricated compatible completely with standard n-well
CMOS technology. It is composed by a combination of a forward biased p<sup>+</sup>-n junction controlling by gate voltage and a
poly-Si/ultrathin oxide/Si tunneling junction. The experimental results demonstrates that: (1)The optical emitting power
of LED increases with both forward p<sup>+</sup>-n junction current increasing and positive gate voltage increasing; (2) The optical
emitting power of LED still increases with gate Voltage increasing while p<sup>+</sup>-n junction forward current at zero; (3) The
spectra of the optical output power on wavelength λ occurs a peak near 1000nm. The results can be explained from the
enhancement on the p-n junction forward current by the gate voltage induced barrier lowering effect and the
S(poly-Si)OS tunneling junction theory.
The earlier astable multivibrator formed by silicon tunnel diode has the disadvantage of low speed and non-modulation.
NDRHBT is a novel type of HBT with NDR characteristics and high speed. Its NDR characteristics can be modulated by
the base voltage V<sub>BE</sub> or base current I<sub>B</sub>. So the astable multivibrator formed by NDRHBT has the advantage of high
speed, high frequency, bistability, and frequency modulation by V<sub>BE</sub> or I<sub>B</sub>. Thus, it can be applied widely in high
frequency oscillation circuits and high speed-digital circuits.
In this paper, it is demonstrated that the frequency of the astable multivibrator can be modulated by base voltage V<sub>BE</sub>.
The experimental result shows that the frequency of time interval between two adjacent pulses f<sub>1</sub> varies from 7×10<sup>4</sup>Hz
down to 2.5×10<sup>4</sup>Hz as V<sub>BE</sub> changes from 4.5V to 6.5V and exhibits near a linear relationship. So it is can be used as an
efficient voltage controlled frequency modulator for pulse signal in high speed digital circuits.
In this paper, it is reported that the design and fabrication of high-brightness and high-power
InGaAlP single-side red LED with electrodes which are interdigitated with the fingers.
High-brightness and high-power InGaAlP LED is a new kind of visible light LED developed in
recent years, which is driven by large current capacity, high luminous efficiency and excellent heat
resistance. It has been used in various fields, such as large area displays, traffic lights, brake lights
and so on. As compared with the conventional double-side LED, the single-side LED is more
flexible to integrate with other devices and its fabrication is simplified.
The size of chip is 1mm<sup>2</sup>. The fabrication of single-side LED, essentially, is the same as
conventional LED, involving photolithography, PECVD SiO<sub>2</sub>, wet etching, evaporating, lift off
and rapid thermal annealing using four masks. To control the widths of mesa and N electrode
precisely, the selecting etch technique has been adopted, using HCL: H<sub>2</sub>O:H<sub>2</sub>O<sub>2</sub> as the InGaAlP
I-V characteristics, light emission spectrum, luminous flux, luminous intensity and luminous
efficiency of this LED have been measured. The characteristics are obtained with turn-on voltage
of 1.5V and forward current of 400mA at its forward voltage of 3V. The peak wavelength is
635nm, which corresponds to red light, and the Full Width of Half Maximum is 16.4nm at
injection current of 350mA. The luminous intensity is 830 mcd. The color coordinates is x=0.6943,
y=0.3056 and the color index is 18.4. So we will conclude that the high-brightness and
high-power InGaAlP single-side red LED will become new focus in both scientific research and
industrial investment for its wide application.
A new simplified heterojunction phototransistor (HPT) circuit model is given in this paper. Most of papers use Ebers-Moll model to describe the optical-electrical relations of HPT. Which is a physical based model and must be changed with different device structure. In this paper, an empirical model is employed. This model mainly formed by three parts: the photo current (I<sub>ph</sub>), base current (I<sub>b</sub>) and collector current(I<sub>c</sub>). A dependent current source is used to model the photo current between the collector and base. The photo current can be different from different optical power. Ib are depend on base-emitter voltage while Ic is a function of collector-emitter voltage, I<sub>b</sub> and I<sub>ph</sub>. Contrast with the Ebers-moll model, the empirical model greatly reduced the complexity of the circuit. The model parameters are extracted on measured Ic-Vce and gummel plots. Then, dates in some documents were used to test the empirical model. There is a good agreement with the measured results.
Bipolar/MOSFET hybrid mode lateral transistor is a transistor in which both bipolar and MOSFET currents flow simultaneously. Because of (1) Good compatibility with CMOS technology; (2) Larger current driving capability and transconductance than MOSFET. So, it is suitable to be taken as a bipolar device in BiCMOS element. In this paper, the Si/SiGe heterostructure, under the gate, is introduced into the conventional bipolar/MOSFET hybrid mode transistor. So a hybrid mode transistor with a lateral n<sup>+</sup>-Si/p-SiGe/n<sup>+</sup>-Si structure parallel in base is formed, in which the heterostructure of E-B junction n<sup>+</sup>-Si/p-SiGe has a high injection electron current from E to B region and a low injection hole current from B to E region (result in by higher barrier for hole), then the total injection efficiency will increase. When this effect becomes a main mechanism than that of the barrier lowering in the surface depletion layer, the characteristics of the device will be dependent on the parameters of SiGe alloy, such as the mole number of Germanium etc. The device simulation of Si/SiGe heterojunction base hybrid mode transistor has been carried out by MEDICI program. The simulation results show that <i>I<sub>C</sub></i> and <i>h<sub>FE</sub></i> increase with Mole number of Ge increasing and <i>W<sub>B</sub></i> decreasing, then the current gain and current capability are improved than that of conventional bipolar/MOSFET hybrid Mode transistor.
Titanium film with about 3nm thickness is deposited on SiO<sub>2</sub>-Si substrate with dual facing targets sputtering method. Nano-oxidation lines are fabricated on this Ti film with various biased voltages and for the first time, current monitoring is performed during the oxidation process using a contact-mode AFM. In the cases of all lines, a flow of current began immediately when the biased voltage was applied and it kept almost unchanged as each of the oxide line was growing. The level of detected currents during the fabrication of oxide lines on Ti film is in the microampere (μA) level. The detected currents increase linearly with the biased voltages, which indicates that the detected current is mainly tunneling current. Thus, the process of nano-oxidation of Ti film is controlled either by the tunneling of electrons or holes through the Ti/water interface.
In this paper, the photo-detected and controlled functions based on silicon photo-electronic Lambda transistor (PLBT) are reported. PLBT is composed of a npn vertical bipolar transistor as main device and a enhancement-mode MOSFET transistor as feedback device which connected in parallel across the base and collector terminals of bipolar transistor. Photo-electronic-lambda bipolar transistor (PLBT) is one important member of Si-photo electronic negative resistance devices. It has wide applications in photo-electronic coupler, light detector, light sensor and other photo-electronic circuit modules, which is significant for the further study of photo-electronic devices and circuits. When the Si-photo-electronic negative transistor device works as a load, it has two stable output states (bistability characteristics) with the change of the input light signals. Using the photo-bistable and self-locking characteristics of the PLBT, a photo-controlled Bistable Logic Circuit Element has been set up successfully. Through detail studying and analyzing to the operation feature and load feature of the photo-controlled bistable circuit, the nonlinear characteristic of the circuit is demonstrated. Furthermore the applications of this circuit element have been studied and verified.
Photo-generated carriers' transmission delay of a CMOS-Process-Compatible double photo-diode (DPD) is analyzed by using device simulation in this paper. The carriers' transmission delay of a DPD in CMOS N-well process consists of three parts: the delay in the P<sup>+</sup> region, in the depletion region and in the N-well. The DPD equivalent circuit model, including photo-generated carriers' transmission delay, is given by means of device simulation. By comparing with different depth of the N-well and different area of the DPD, the delay of the diffusion part in the N-well and the delay of the junction capacitance are the most significant factors to determine the delay time of a DPD. In addition, the diffusion delay is relative to the depth, the doping concentration of the N-well and the bias. Adopting smaller size CMOS process is of benefit to improving the speed due to the shallow well, nevertheless the shallow well can cause the responsivity reduce. The responsivity reduce can be compensated by increasing the junction area.
We have measured the I-V characteristics of the Resonant tunneling diode (RTD) fabricated by ourselves. Basing on the measured results, several questions have been analyzed and discussed: (1) Temperature effects on I-V characteristics; (2) “The Apparent positive resistance phenomena” in negative resistance region. The analysis and discussion on above questions are very useful and helpful for design and fabrication of RTD.
Lattice-matched InGaP on GaAs substrate was successfully grown by solid-source molecular beam epitaxy (SSMBE) with a GaP decomposition source. 0.5um-thick InGaP epilayer shows photoluminescence (PL) peak energy as large as 1.962eV, PL FWHM as small as 9.4meV, X-ray diffraction (XRD) rocking curve line-width as narrow as 25arcsec. The electron mobility of undoped, Si-doped InGaP layers measured by Hall are comparable to similar InGaP/GaAs heterojunction grown by SSMBE with other source or other growth techniques. Then the InGaP/GaAs HBT epiwafer is grown by this way. Beryllium(Be) diffusion is reduced by increasing the As/Ga flux ratio. Heterojuction Bipolar Transistor (HBT) with 75×75um<sup>2</sup> emitter mesa area fabricated using this structure yielded an excellent performance with high current gain. The results reveal that InGaP/GaAs heterojunction grown by the present growth way have great potential application for semiconductor devices.
With the development and application of nanofabrication on nano photoelectron device, the completely oxidized thin metal film such as titanium film by Atomic Force microscope (AFM) tip induced oxidation method has been used to make various nano electric devices. It is more and more important to study the process mechanism for improving the operational stability and reliability of such nano devices. In this paper, the mechanism of AFM tip induced oxidation is analyzed with several aspects. According to the experimental results of AFM tip induced oxidation of titanium under various voltage biases and scanning speeds, we find that the height of the titanium oxidation is linear with the voltage bias and with the negative log of the scanning speed. Based on the formers’ theories, the mechanism and the theoretical modeling of AFM tip induced oxidation are improved. By setting the proper conditions such as voltage bias of 8V and
scanning speed of 0.1μm/s, good nanofabrication results with AFM oxidation of titanium are got and the oxide lines are with good aspect ratio and good continuity.
By photo-sensitizing the surface controlled negative impedance transistor (NEGIT), we can get a novel photo-negative resistance device--- photo-surface controlled negative impedance transistor--- PNEGIT, PNEGIT has a photo-surface controlled negative resistance I-V characteristics.
By taking PNEGIT as an Optical input device to form a drive device and a resistor R<sub>L</sub> to form a load of the inverter. And taking a LED in series with R<sub>L</sub> as an optical output device. Due to the Instability at the state in the negative resistance region. A photo-controlled Bistability can be made. The state in the valley current region will jump suddenly to the state in the positive resistance region or jumps in the opposite direction as the optical input power p<sub>in</sub> increases or decreases respectively.
It is demonstrated that, there are two states of photo current or optical output power p<sub>out</sub> corresponding one State of p<sub>in</sub> Value. This optical Bistability has the function of optical switching, optical self-latching, and optical memory. It can be Applicated in the area of optical information processing, optical computing and optical communication in coming days.
The Resonant tunneling diode (RTD) is a high speed nanoelectronic device based on quantum resonant tunneling effect. It has the advantage of high frequency, low operating Voltage, low power dissipation, negative resistance, bistability and self-latching. It can be applied in high speed integrated circuits widely.
Based on the analysis of correlation between the device characteristic parameters and the material structure parameters, some design rules have been summarized as following:
1. The barrier width L<sub>B</sub> of RTD should be selected as narrow as possible to increase the peak current density J<sub>p</sub>.
2. The well width L<sub>W</sub> should be selected slightly wider to decrease the peak Voltage V<sub>p</sub>.
3. The spacer width L<sub>S</sub> should be selected slightly narrower to decrease the peak Voltage V<sub>p</sub>.
4. The emitter doping density N<sub>E</sub> should be determined to a reasonable value to avoid both R<sub>S</sub> and intrinsic capacitance C<sub>d</sub> too much.
5. Selecting AlAs as the barrier material to increase the barrier height then to increase peak valley current ratio (PVCR).
6. In emitter region, adding a narrow bandgap material layer to form a subwell. The 3dimension/2dimension resonant tunneling changes to 2dimension/3dimension resonant tunneling, the PVCR will be improved.
From above design rules, The GaAs based MBE material structure of RTD has been designed, The RTD devices have been fabricated from this material structure shown very good performance. Main characteristic parameters listed as following: Room temperature PVCR 7.6, f<sub>R</sub>=54GHZ, switching time t<sub>r</sub>≈171ps.
We first proposed monolithic optoelectronic integration of Resonant Tunneling Diode (RTD) and Heterojunction Bipolar Phototransistor (HPT). Circuit simulations using simple models of RTD and HPT successfully produced the optoelectronic bistable characteristics of RTD and HPT Negative Differential Resistance (NDR) device. The basic operation mechanism of Photoelectric Monostable-Bistable Transition Logic Elements (PMOBILE's) by utilizing the functionality of two series-connected RTDs in combination with HPT is also demonstrated by simulation.
On replacing the npn bipolar transistor by a npn phototransistor in the Lambda Bipolar transistor (LBT), we can get a novel optoelectronic negative resistance detector -- photo-Lambda bipolar transistor (PLBT). In this paper, the photo-negative resistance characteristic of this device has been demonstrated by PSPICE simulation and by a fabricated experimental device. It is shown that PLBT is not only a conventional optical detector but also a basic element in the photo-induced oscillators and in the photo-controlled frequency modulator. A wide variety of application for PLBT can be expected. PLBT is composed of a npn phototransistor as main device and a n-channel enhancement-mode MOSFET as a feed back device which connected in parallel across the base and collector terminals of phototransistor. As the V<sub>CE</sub> of photo-transistor (as same as V<sub>GS</sub> of MOSFET) is in excess of threshold voltage V<sub>T</sub> of MOSFET, then the MOSFET turns on and its drain current I<sub>d</sub> will shunt the photo-base current I<sub>phb</sub> and the collector photocurrent I<sub>ph</sub> will decrease. The photo-negative resistance characteristic of PLBT will arise. The expressions of I<sub>ph</sub> and negative resistance R<sub>N</sub> have been derived from the physical model of PLBT. The simulation results of PSPICE are in agreement with measured data of the experimental PLBT device.
By encapsulating a light emitting diode (LED) with a Silicon photo-negative resistance Device face to face in a hermetic package, a new type opto-isolator has been developed. Because of the features of Bistability and self-latching on the silicon photo-negative resistance devices, these non-linear opto-isolators present the response persistence function for the input signal. In this paper, the demonstration of response persistance function on PDUBAT type of silicon photo-negative resistance device has been made experimentally. The Dual Base Transistor (DUBAT) is a three terminals Voltage controlled negative resistance device, it is composed from the combination of a pnp type lateral bipolar transistor and a npn type vertical bipolar transistor. As DUBAT is radiated by light, the npn bipolar transistor is taken as a phototransistor. Thus the DUBAT will become a photo-DUBAT or PDUBAT. In PDUBAT, it is found that the photo-controlled "S" negative resistance characteristic can introduce a photo-controlled current switching effect and the persistance response functions, which keeps the response state for the input light signal until the reset signal changes the circuit from maintaining state to waiting state.
By using mixed-mode simulator in ATLAS, a commercial simulator produced by Silvaco International, a CMOS-process-compatible opto-electronic integrated circuit (OEIC) receiver is designed. The OEIC receiver can be used in optical communications or optical interconnections. The optical wavelength response, optical frequency response and optical pulse response of the OEIC receiver are simulated in 0.35 μm and 0.6 μm CMOS process. The sensitivity and the bandwidth of the OEIC receiver are optimized in giving detector area. Available receiver bandwidth is optimized under the given input optical power and detector area. The feedback voltage in trans-impedance amplifier is designed both for bandwidth and for sensitivity. The OEIC receiver was fabricated with a 0.6 μm CMOS process through MPW (multi-projector wafer) in China.
Photoelectronic DUal Base Transistor (PDUBAT) is a novel kind of photoelectronic negative resistance devices, which features 'N' type negative resistance and small negative resistance R<SUB>N</SUB>. PDUBAT consists of a vertical NPN bipolar transistor and a P type diffusion region with large area over a specific distance. The base and collector of the vertical NPN BJT with a large P diffusion region form a lateral PNP BJT. The emitter and collector of the vertical NPN BJT are connected to the ground and voltage supply respectively, while the P diffusion region is left floated to detect input light signal. When the device is exposed to light, a large number of electron-hole pairs are generated at the PN junction under the P diffusion region. The holes travel along the base of the lateral PNP BJT and become the driving current of the vertical NPN BJT. In experiments, we found that PDUBAT acts as a pulse oscillator without the load of inductors, whose frequency and magnitude are modulated by the intensity of incident light. The oscillating frequency increases while the magnitude decreases with the increasing of light intensity. The manufacturing process of PDUBAT is compatible with that of JBTs, so that it can be incorporated with the ICs.
We report on optoelectronic multiple chip modules, consisting of vertical cavity surface emitting laser (VCSEL), photodetector and 1.2 micrometer CMOS electronic circuit. The hybrid integrated components operate at a date rate of 155 Mb/s, which could be used in optical interconnects for multiple computers.